The oligomerization of lower alpha olefins is of industrial concern as many polymers of alpha olefins such as ethylene and propylene comprise a higher alpha olefin such as butene, hexene or octene. If ethylene could be selectively oligomerized at relatively high conversion to a higher alpha olefin such as butene, hexene or octene it would mean that a plant need only have one monomer, such as ethylene, from which co-monomers could be produced.
There have been a number of attempts to oligomerize alpha olefins into higher alpha olefins.
There are a number of papers and patents in which Kingsley John Cavell and/or Anthony J. Masters is/are named as an author(s) (e.g. WO 8302907) in which square planar complexes of Ni.sup.2+ are used to oligomerize alpha olefins. The complexes contain triphenyl phosphine and 2,4-pentanedithione (sacsac) or 4-thioxo-2-pentanone. These compounds are not the dithiophosphinate precursors of the present invention.
U.S. Pat. No. 4,533,651 issued Aug. 6, 1985 assigned to Commonwealth Scientific and Industrial Research Organization, Australia, also discloses oligomerization of ethylene with a nickel complex which contains a phosphine. The patent does not suggest the use of a ligand which contains both a phosphine and an imine or a dithiophosphinate ligand of the present invention.
Related U.S. Pat. No. 5,286,696 issued Feb. 14, 1994 and 5,210,360 issued May 11, 1993 both assigned to Phillips disclose the oligomerization of ethylene using a nickel complex which contains a phosphine. The patents do not disclose the presence of both a phosphine and an imine group or a dithiophosphinate in the ligand.
U.S. Pat. No. 5,334,791 issued Aug. 2, 1994 to Ligands, Inc. discloses that some of the catalyst precursors of the present invention may be used to hydrogenate non-aromatic unsaturated hydrocarbons. U.S. Pat. No. 5,352,813 issued Oct. 4, 1994 to the University of Alberta discloses that some of the catalyst precursors of the present invention may be used to carbonylate methanol. However, these patents do not disclose that such compounds in conjunction with an activator of a compound such as aluminum or boron could be used to oligomerize alpha olefins. Further these references do not teach or suggest that such an oligomerization if possible would have a high conversion and a controllable selectivity.